The present invention relates to a deformable, shrinkable fiber that is stable at body temperatures in the dry state but shrinks and distorts when it contacts body fluids such as urine and menses which are at body temperature in the wet state. The present invention also relates to a process for making the fiber and articles made of the fiber.
There is a continual desire to develop thinner diapers, feminine hygiene products, and adult incontinent products. A thinner product is less bulky to wear, fits better under clothing, is less noticeable and is more compact to package and carry. However, a problem exists which inhibits the development of thinner diapers, feminine hygiene products, and adult incontinent products. This problem is commonly referred to as xe2x80x9cgel blocking.xe2x80x9d Gel blocking occurs when particles of a superabsorbent polymer (xe2x80x9cSAPxe2x80x9d) are wetted and the particles swell, inhibiting fluid transmission to other regions of the absorbent article. Leakage from the absorbent article can occur before achieving maximum use of the SAP or before the fluid can diffuse past the blocking particles into the remainder of the absorbent article. Gel blocking typically occurs in absorbent articles containing high levels, typically 30 to 40%, of SAP and higher. SAP is typically blended with cellulose fluff pulp or modified cellulose pulps. The problem is most prevalent when the level of SAP exceeds 40% by weight in these blends. The continuous barrier formed by the gel prohibits additional penetration of the structure by more fluid, thus sealing much of the SAP from the fluid. The end result is that the maximum benefit of the product is not achieved.
U.S. Pat. Nos. 4,235,237; 4,381,782; 4,500,315; 4,573,988; 4,699,823; 4,935,022; 5,180,622; and 5,643,238 disclose various attempts to reduce gel blocking and its impact on fluid acquisition and storage.
The articles of the present invention employ shrinkable fibers yet eliminate gel blocking. Attempts have been made in the past to use shrinkable fibers in products such as diapers but such attempts have been unsuccessful in eliminating the problem of gel blocking.
U.S. Pat. No. 4,357,938 discloses a disposable diaper comprising a water-absorbing layer located between a liquid-permeable surface sheet and a liquid impermeable backing sheet, wherein water-absorbing shrinkable fibers are fixed to and extend along the central portion in the lengthwise direction of the disposable diaper in such a manner that the water-absorbing shrinkable fibers are not placed on top of the water-absorbing layer, and wherein means is provided so that the water-absorbing shrinkable fibers become wetted when the diaper is wetted, the water-absorbing shrinkable fibers exhibiting a percent shrinkage of at least 15% and a shrinking force of at least 100 g when the fibers are wetted.
U.S. Pat. No. 4,447,240 discloses a disposable diaper which comprises a liquid-permeable surface sheet, a liquid-impermeable back face sheet and a water-absorbing layer disposed between said sheets, wherein water-absorbing shrinkable fibers, the length of which is reduced on contact with water to impart elasticity to the fibers, are fixed across the central portion in the lengthwise direction of the disposable diaper without being lapped over the water-absorbing layer and the water-absorbing layer is connected to said water-absorbing shrinkable fibers by cellulose fibers.
U.S. Pat. No. 4,942,089 discloses a rapidly shrinking fiber made from modified polyvinyl alcohol wherein the fiber is capable of rapidly shrinking when coming into contact with water at ordinary temperature and capable of maintaining the fiber form and exhibiting rubber elasticity.
U.S. Pat. No. 5,567,796 discloses a polyester filament or fiber, when drawn under selected conditions, has a high shrinkage ratio but also a high shrinkage stress.
In contrast to the patents cited above, use of the fibers of the present invention will enable development and production of thinner absorbent products as well as more efficient use of SAP in existing products by reducing the effects of gel blocking.
The present invention relates to a deformable, shrinkable fiber that is dimensionally stable at normal body temperatures of approximately 37xc2x0 C. in the dry state, but is dimensionally unstable (i.e. shrinks and distorts) when wet at the same temperature.
In one embodiment of the present invention a fiber forming polymer is selected that has a dry glass transition temperature (xe2x80x9cdry Tgxe2x80x9d) of greater than or equal to 42xc2x0 C. and a wet glass transition temperature (xe2x80x9cwet Tgxe2x80x9d) of less than or equal to 32xc2x0 C.
The present invention also relates to a method of preparing said shrinkable fiber, and an absorbent article(s) comprising said fiber.